I assume you are finding this 'error' in the syslog.log file? What is the impact to your operations?
The vsantraced is a service that monitors vSAN operations and would be a requirement for getting the vsanObserver to run. vsanObserver is performance monitoring tool and each host participating in a vSAN cluster will collect performance data in the background using this service.
There are scheduled cron jobs that run in the background on your ESXi and these include the performance collection job for vSAN. You can find the cron job configuration at /var/spool/cron/crontab/root. In this file are all the scheduled tasks that ESXi will run, including the vsanObserver.sh, which is scheduled to run every 2 minutes. If vSAN is not running, the necessary daemons will not be running resulting in the errors you are seeing. These 'errors' can be safely ignored as they do not indicate a problem, not should they be causing any impact.
"Although we don't have vSAN installed on our VmWare" - vSAN is built into the vmkernel and thus is present in every ESXi installation (from 5.5 onwards).
If you do not have vSAN enabled then logging messages such as these referencing vSAN-daemons can be safely ignored.